Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1246 PM EST Sun Jan 05 2020 Valid 12Z Wed Jan 08 2020 - 12Z Sun Jan 12 2020 ...Heavy Rain Threat from the Lower Mississippi to Ohio Valleys Fri-Sat... ...Overview/Guidance Assessment... Guidance continues to advertise an amplified mean trough aloft for the western U.S., between ridges over the east-central Pacific and the Southeast U.S.. The Climate Prediction Center 8-14 Day forecast still suggests some variation of this pattern may persist well beyond the end of the medium range period. Evolution aloft and surface features will lead to a heavy rain threat most likely from the Lower Mississippi Valley through the Tennessee Valley and Ohio Valley. Teleconnections relative to the positive height anomaly center which multi-day means show near or offshore the East Coast later in the period also target this area for greatest precipitation potential. Meanwhile North Pacific energy feeding into the mean trough will bring episodes of enhanced precipitation with best focus over the Pacific Northwest. Forecast spread at medium range time scales has decreased since yesterday, bolstering forecast confidence. GEFS/NAEFS/ECMWF ensembles are now more in line with the ECMWF/UKMET/Canadian and GFS, now that the 12 UTC GFS has trended to a less progressive CONUS solution late week to next weekend. Favor a guidance composite of these solutions that maintains good WPC continuity. ...Weather Highlights/Threats... A lead low/system tracking off the New England coast Wed will strengthen as it heads into the Canadian Maritimes and support wrapback snows and a period of breezy conditions in its wake. Upstream, a northern Plains to eastern Canadian system Wed-Fri will wrap some moderately heavy snows into a cooled northern Plains/Upper Midwest/Great Lakes. Confidence is increasing for the potential of a heavy rainfall event from the Lower Mississippi Valley into the Tennessee Valley and Ohio Valley late this week into the weekend. The cold front trailing from late week Plains-eastern Canada system will have several embedded waves and may progress fairly slowly for a time while awaiting upstream western energy aloft. Two or three days of Gulf inflow ahead of this wavy front would provide considerable moisture to enhance rainfall amounts and some embedded convection is possible. This area encompasses some locations that recently received significant rainfall, so effects from this upcoming event will require close monitoring. There is a growing a signal for wintry precipitation on the northern periphery of the moisture shield, and significant accumulation probabilities are trending up. Over the West, still expect highest totals of rain/mountain snow over the Pacific Northwest coast/northwest corner of California as well as the Cascades, with a secondary maximum over the northern Rockies. Some moisture will extend southeastward but with lighter amounts in most cases. Heaviest precipitation should occur from Fri into the weekend, though amounts are likely not to be extreme given fairly modest precipitable water anomalies. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml